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Go tohttp://www.wdtb.noaa.gov/courses/EF-scale/index.htmlfor more information regarding EF-Scale training by the WDTB.
To view the Enhanced Fujita Scale Document, go tohttp://www.depts.ttu.edu/nwi/Pubs/FScale/EFScale.pdf

Dr. T. Theodore Fujita first introduced The Fujita Scale in theSMRP Research Paper, Number 91, published in February 1971 and titled,"Proposed Characterization of Tornadoes and Hurricanes by Area andIntensity".Fujita revealed in the abstract his dreams and intentions of theF-Scale.He wanted something that categorized each tornado byintensity and area.The scale was divided into six categories:

• F0 (Gale)
• F1 (Weak)
• F2 (Strong)
• F3 (Severe)
• F4 (Devastating)
• F5 (Incredible)

Dr. Fujita's goals in his research in developing the F-Scale were

• categorize each tornado by its intensity and its area
• estimate a wind speed associated with the damage caused by the tornado

The United States today averages 1200 tornadoes a year.The number of tornado reports increased dramatically in the 1990s as themodernized National Weather Service installed the Doppler Radarnetwork.The National Weather Service modernization also beganthe Warning Coordination Meteorologist program increasing partnershipswith media and Emergency Management across the United States.This program also initiated the training of storm spotters across theCounty Warning Area of each Weather Forecast Office.With more people trained to relay information on storm activity to the WeatherForecast Office and improved communication and digital technology, moretornadoes could be reported.

While the Super Outbreak of tornadoes was the spring board for theF-Scale, it was the Jarrell, TX tornado of May 27, 1997 and theOklahoma City/Moore, OK tornado of May 3, 1999 that brought to theforefront the problem that maybe the wind estimates were too high inthe F-Scale.Meteorologists, Emergency Managers and Engineers convened on Moore,OK to study the weaknesses in the structures destroyed by thetornado of May 3, 1999.The findings can be found in the documentFEMA 342,Building Assessment Report, MidwestTornadoes of May 3, 1999, Observations, Recommendations and TechnicalGuidance.That document can be foundhere.Engineers claim that many homes are rated to withstand winds to 100mph.Therefore, the question was raised that if a tornado hasover 200 mph winds, how can the structure reveal this estimate whenmuch of it is gone?

The Fujita Scale is a well known scale that uses damage caused bya tornado and relates the damage to the fastest 1/4-mile wind at theheight of a damaged structure.Fujita's scale was designed to connect smoothly the BeaufortScale (B) with the speed of sound atmospheric scale, or Machspeed (M).Fujita explains explicitly that "F-scale winds are estimated fromstructural and/or tree damage, the estimated wind speed applies tothe height of the apparent damage above the ground."Figure 1 shows graphically the relationship between the three scales.

From this graph, Fujita then released the following descriptions forthe F-Scalehttp://www.spc.noaa.gov/faq/tornado/f-scale.html.


Over the years, the F-Scale has revealed the following weaknesses:

• It issubjective based solely on thedamage caused by a tornado
• No recognition in difference in construction
• Difficult to apply with no damage indicators
• if the 3/4-mile wide tornado does not hit any structures, what F-scale should be assigned?
• Subject to bias
• Based on the worst damage (even if it is one building or house)
• Overestimates wind speeds greater than F3

And the F-Scale has had its misuses over the years:

• Too much reliance on the estimated wind speeds
• Oversimplification of the damage description
• Judge the F-scale by the appearance of the tornado cloud
• Unrecognizing weak structures
• mobile homes
• modified homes

Fujita recognized that improvement was necessary.He published his memoirs calledMystery of Severe Stormsin 1992 updating the Fujita Tornado Scale to include an estimateof f-scale damage then selecting the F-scale asa combination of f-scales and types of structural damage.

For example, if a tornado knocks down the walls of an area of homes.If it is determined that the walls collapsed, then the damage assignedis F3.If it is a brick home, then that lowers the damage to F2.Then, according to the table since it was a brick structure,then you +1 making the rating F3.

When the committee met to develop the Enhanced Fujita Scale (seeoriginal document) one point was made very clear:it must continue to support and maintain the original tornado database.;In other word, there must be some conformity to that of the F-Scalethat is listed in the database.Other ideas were agreed to including:

• Consistent Assessment of Damage
• enhance description of damage with examples and photos
• include not only structures, but also vegetation
• base damage assignment on more than one structure, if available
• develop a PC-based expert system
• develop training materials
• Data Collection
• maintain current tornado database
• surveys should include additional data
• mean and maximum damage path width
• basis for damage assignment
• latitude/longitude of where the path began and ended
• number of hours spent on the damage survey
• names of survey team member(s)

When using the EF-Scale to determine the tornado's EF-rating,begin with the28 Damage Indicators.Each one of these indicators have a description of the typicalconstruction for that category of indicator.Then, the next step is to find theDegree of Damage (DOD).Each DOD in each category is given and expected estimate of wind speed,a lower bound of wind speed and an upper bound of wind speed.

Let's take the earlier example, a tornado moves through a neighborhoodand walls are knocked down of an area of homes.Here the Damage indicator would be #2, One or Two Family Residences (FR12).The typical construction for this fits being a brick veneer sidinghome.The DOD would be a 8, most walls collapsed in bottom floor.Thus, the estimated winds would be 127 - 178 mph with theexpected wind speed of 152 mph.Now, taking this number to theEF-Scale,the damage would be ratedEF-3 with winds between 136 - 165 mph.